Mucosal regeneration following injury involves restoration of normal regional patterns of functional and morphological gut differentiation and is a characteristic pathological feature of many gastrointestinal diseases including inflammatory bowel disease. The fibroblast growth factors (FGFs) are an important group of regulatory molecules that mediate a number of morphogenic processes occurring during embryogenesis, during fetal development, and during wound-healing. The central hypothesis of this proposal is that members of the FGF family play a pivotal role in the regulation of epithelial injury-repair in IBD. The long term goals of this project will be to use in vitro, in vivo, and transgenic model systems to define the roles of FGFs in regulating epithelial differentiation, cell- renewal, and mucosal regeneration in IBD. The specific aims of the proposal are: specific aim 1) To determine the patterns of FGF receptor and ligand expression in IBD; specific aim 2) To characterize the patterns of FGF receptor and ligand expression in in vivo mouse models of IBD and mucosal injury-repair; specific aim 3) To determine the effects of FGFs on intestinal epithelial cell function and differentiation and to determine the effects of cytokines on expression of FGFs and FGF receptors in intestinal epithelial cells in culture. FGF receptor and ligand expression will be determined in normal tissue samples from patients with inflammatory bowel disease using RNase protection analysis. Cell-specific patterns of FGF receptor expression will be determined by immunohistochemistry and in situ hybridization. The effects of exogenous FGFs on cellular differentiation of intestinal epithelial cells will be examined using Caco- 2 cells as a model system. The role of FGFs in regulating integrin expression will be examined. The effects of altering FGF mediated signal transduction during differentiation of Caco-2 cells will be analyzed using cell lines transfected with plasmids expressing either the normal FGF receptor 1 sequence or a dominant-negative mutant form of the receptor that is capable of inhibiting signal transduction by endogenous FGF receptors. The effects of inflammatory cytokines on FGF receptor expression will also b e determined in undifferentiated and differentiated Caco-2 cells. The expression of FGFs and their receptors will be characterized during mucosal regeneration using a radiation-injury model and in dextran sulfate induced colitis.